1. Field of Invention
The present invention pertains to the field of distributed systems. More particularly, this invention relates to time synchronization among clocks in a distributed system.
2. Art Background
Distributed systems are commonly arranged as a collection of nodes which are interconnected via one or more network communication links. These network communication links may be packetized links such as Ethernet or one or more of a variety of other packetized links that are adapted to distributed control system applications.
Distributed systems commonly benefit from precise control of the timing at the distributed nodes. U.S. Pat. No. 5,566,180 of Eidson et. al. teaches a method and apparatus for providing precise control of timing in distributed nodes by synchronizing the local clocks in the distributed nodes. The synchronization protocol of Eidson et. al. involves the exchange of timing data packets and follow up packets among the nodes so that the delay in the transfer of a timing data packet from a first node to a second node in combination with timing information in a follow up packet can be used to accurately adjust a local clock in the second node.
A variety of conditions that are commonly found in distributed systems may introduce variation or jitter in the delay in the transfer of a timing data packet. For example, communication circuitry at various points in the distributed system may introduce jitter. In addition, communication circuits such as gateways can introduce jitter that depends on the volume of traffic in the system. Unfortunately, such jitter may reduce the accuracy of time synchronization in a distributed system.